X-Rank Hunter

E-rank? A-rank? S-rank? SSS-rank? "I already heard all of them", but "X-rank?" it's unheard-of.

1,000 years ago, great calamities fell down on Earth. Natural disasters, wars and plagues has occured and bring forth destruction. Later, an "incurable virus" spread out all over the world and put humanity to the verge of extinction. Billions of people died... and all of these happened in only "one year".

When the hopes of humanity almost died out, a "star" has fallen fron the sky and opened the gate of "abyss". Subsequently, portals that connected to the "other world" appeared all over the Earth. Monsters came out from the abyss and from the portals to wreck havoc on Earth.

Humanity completely lose their hope, but the "virus" that they considered as a "curse" became a "blessings" to them. Through the virus they had suffered, humanity have had "awakened" a power that enabled them to fight and hunt beasts.

Since then, they managed to survive.... those who had awakened their powers called themselves as "Hunters".

The highest rank that the hunter could ever reach is "SSS-rank", but "X-rank?" what is that?